— 7 — 



the olive, wax of plants, etc. The fats of herbaceous vegetables have 

 less value than those of seeds and fruits. 



DIGESTIBILITY OF FOODS. 



Upon the basis of the preceding we can proceed intelligently with 

 the next step, which is to consider the digestibility of the different 

 foods. If the total amoimt of each food introduced into the body was 

 digestible, the whole subject of feeding would be very much simplified. 

 But, 011 the contrary, in all foods there is a certain portion of each 

 nutrient, whether it be protein, fat, or carbohydrate, which is notdigested 

 or assimilated. A large niimber of experiments have been made in 

 this direction, most of them in Germany. 



In Order to ascertain how much of the food is not digested, the food 

 is weighed and analyzed before consumption, and the weight and com- 

 position of the excrement is also determined. 



The difference between the two analyses is taken as the quantity 

 digested or assimilated. The results so obtained are termed digestioyi 

 co-eßcients, and are only approximate, but in the present state of such 

 researches, they are the best data available. Besides these direct experi- 

 ments on the body, others have been made in the laboratory with success, 

 in which the gastric juice derived from animals has been employed. This 

 cannot be so easily done in the case of man, as the normal gastric juice 

 from human subjects is not ordinarily obtainable. 



An animal can be fed on one kind of food for a given time and suffer 

 no inconveniences in any way whatever, and, in all probability, would 

 relish it. Quite the contrary would be the case with man. The most 

 palatable food would, if fed alone, become exceedingly distasteful to 

 him and tend to disarrange bis digestive functions if fed for five or six 

 days in succession; and thus, at the time when data on the digestibility 

 and amount necessary of the food should be obtained, the System of the 

 man might be in such a condition that the data would be unreliable. 

 Again, for each food-material the digestion coefficient may vary con- 

 siderably with different persons; still the more nitrogenous or easily solu- 

 ble is the food, the higher, as a rule, is the digestion coefficient. Nearly all 

 of the protein of ordinary meat, fish, and milk is readily digested; that 

 of potatoes, whole wheat, and rye flour, one fourth or even one third 

 may not be absorbed by the body. About 95 per cent of the fats from 

 butter, milk, oils, and such foods is digestible. The vegetable fats vary 

 from about 50 to 75 per cent; that is, the digestion coefficient would be 

 from 50 to 75. Sugar is supposed to be completely assimilated, and 

 starch nearly so if not used in excess; these two comprise the main 

 parts of the carbohydrates. The fruits and vegetables contain the 

 bulk of the woody fiber. 



The animal foods have in general the advantage of the vegetable, in 

 that they contain more protein, and that their protein is more digestible. 

 Professor Atwater states that the quantity of food digested appears to l)e 

 less affected by flavors, flavoring materials, and food adjuncts, and to 

 differ less with different persons than is commonly supposed. 



Nutritive Ratio. — The different foods vary very much in their com- 

 position; some, such as peas and beans and the meats, contain large 

 amounts of protein or muscle-forming ingredients, and very little of the 



